An important feature of any nucleic acid-based diagnostic assay is the sample preparation method for extracting DNA or RNA from blood, cells or target tissue. A critical requirement of this first step is to obtain a target nucleic acid of sufficient purity and quantity that is suitable for subsequent processes such as amplification or hybridization. Many techniques and methods have been described in the literature for the purpose of isolating nucleic acids. Typically, methods used to obtain DNA utilize detergent action or mechanical treatment for disruption of cells, followed by enzymatic digestion of the protein contaminants with proteases such as Pronase and Proteinase K (see, e.g., Molecular Cloning: A Laboratory Manual, Sambrook, J., Fritsch, E. F. and Maniatis, T. Eds., Cold Spring Harbor Press, 1989). The nucleic acids are then purified by organic extraction with phenol/chloroform, followed by ethanol precipitation of the DNA from the aqueous phase. Other methods of DNA extraction from various tissue sources involve the use of chaotropic salts such as guanidinium isothiocyanate and guanidine hydrochloride--reagents which lyse cells rapidly and are strong denaturants.
Adaptations of the basic approaches outlined above are commonly used for DNA isolation from blood. In a simplification of these procedures, DNA can be obtained from small volumes of blood (.sup..about. 50 .mu.L) by boiling in water in the presence of chelating agents such as Chelex-100 (Bio-Rad Laboratories, Richmond Calif.) and used in PCR reactions (see, e.g., Winberg, G., PCR Methods and Application, 1, 72-74, 1991).